With the development of touch screen technology, touch control technology advances rapidly. Touch control technology is widely used to make touch control display panels by numerous companies. Based on the touch control operation principles, touch screens are divided into different categories: resistive touch screens, capacitive touch screens, infrared touch screens, surface acoustic wave (SAW) touch screens, electromagnetic touch screens, acoustic pulse recognition (APR) touch screens, frustrated total internal reflection (FTIR) touch screens, and etc. Based on the formation structures, touch screens are divided into the following categories: out-cell touch screens (double layers), on-cover touch screens (single layer), on-cell touch screens, and in-cell touch screens.
Meanwhile, the touch screen technology advancement and market demands drive the market trend of having thinner touch display modules. The touch sensing structures are moving away from out-cell touch sensing and towards embedded or integrated touch sensing, which can reduce the thickness of the touch screens as well as substantially reduce the cost of touch screens. Currently, integrated touch screens are divided into three categories: resistive touch screens, capacitive touch screens, and optical touch screens. The resistive touch screens belong to low-end touch sensing technology and may have a short product lifespan. The capacitive touch screens are suitable mainly for small to medium size applications. The optical touch screens may have less limitation on size and may have a prolong product lifespan. Thus, the optical touch control technology may become the mainstream touch sensing technology for the next generation touch screens.